Method for evaluating hydrogen-absorbing alloys for electrode.

Abstract: A hydrogen-absorbing alloy electrode utilizes as an electrode material a hydrogen-absorbing alloy having selectively oriented crystals, which is expressed in terms of a specific maximum value obtained from analysis of powder X-ray diffractometry. This electrode, in which the hydrogen-absorbing alloy used is hardly pulverized upon repeated charge-discharge cycles and oxidation thereof is suppressed, gives metal hydride alkaline secondary batteries having excellent cycle characteristics. A method for evaluating hydogen-absorbing alloys for electrode comprises, utilizing the fact that there exists a clear relationship between specific parameters obtained by analyzing data based on the hydrogen-absorbing alloy to be evaluated and the characteristics of the electrode obtained therefrom, preparing and using analytical curves with the specific parameters. This method can evaluate rapidly and precisely various characteristics of hydrogen-absorbing alloys for electrode, without actually fabricating test cells therefrom.

Description: The present invention relates to a method for evaluating hydrogen-absorbing alloys for electrode material. Hydrogen-absorbing alloys capable of absorbing and discharging hydrogen have been developed actively in recent years. Metal hydride alkaline secondary batteries utilizing these hydrogen-absorbing alloys as negative electrode materials have been attracting much attention and expected to become a mainstream in the next generation, since they are lighter and can be provided with higher capacity as compared to lead, nickel-cadmium and like conventional secondary batteries. Hydrogen-absorbing alloys used for batteries must absorb or discharge hydrogen at near room temperature. Representative examples of these alloys currently in actual use are CaCu 5 -type alloys having a basic structure of LaNi 5 or MmNi 5 . In addition, various studies have been made to commercialize AB 2 -type alloys having a C14Laves structure, which are expected to become of high capacity. The important features of hydrogen-absorbing alloy electrodes are evaluated by determining the degree of activation in an initial stage of cycles, corrosion resistance, initial electrode capacity, charge-discharge cycle characteristics (retention of capacity) and like properties. These evaluations have been made on sample batteries actually prepared with the electrode to be tested. However, since the properties of a hydrogen-absorbing alloy fluctuate with minute variations in its preparation conditions, such as roll surface speed in the liquid quenching process, gas ejection speed in the gas atomization process, cooling water temperature in the casting process and the like, the properties of electrodes prepared therefrom also fluctuate to some extents. Such being the case, in conducting quality control of a production line, it becomes necessary to fabricate batteries for evaluation actually for each production lot and evaluate them for various properties, thereby checking the characteristics of the electrodes. This type of evaluation requires a time-consuming process. There has therefore long been desired development of a method for estimating the characteristics of hydrogen-absorbing alloys as electrode materials rapidly and precisely, without actually fabricating test batteries. In order to realize the above desire, the present inventors have made an intensive study on the properties of various hydrogen-absorbing alloys for electrode. As a result, it has been found that although there exists no distinct relationship between the composition or lattice constant of a hydrogen-absorbing alloy and the characteristics of the electrode obtained therefrom, there does exists clear relationship between specific parameters obtained by analyzing data based on the results of X-ray diffractometry conducted on the hydrogen-absorbing alloy to be evaluated and the characteristics of the electrode obtained therefrom. Accordingly, another object of the present invention is to provide a method for evaluating hydrogen-absorbing alloys for electrodes, which can evaluate the alloys rapidly and precisely. These objects are solved with the features of the claims. A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: FIGURE 1 is a schematic perspective view of one of the test cells fabricated in Examples; FIGURE 2 is a graph showing the relationship between the parameter P A and the capacity retention ratio; FIGURE 3 is a graph showing the relationship between the parameter P B and the capacity retention ratio; FIGURE 4 is a graph showing the relationship between the parameter P A and the degree of activation; FIGURE 5 is a graph showing the relationship between the parameter P B and the degree of activation; FIGURE 6 is a graph showing the relationship between the parameter P A and the capacity retention ratio; FIGURE 7 is a graph showing the relationship between the parameter P B and the capacity retention ratio; FIGURE 8 is a graph showing the relationship between the parameter P A and the degree of activation; and FIGURE 9 is a graph showing the relationship between the parameter P B and the degree of activation. The inventive method comprises the steps of: (1) subjecting a plurality of hydrogen-absorbing alloys M 1 , M 2 , ···, M x for preparing analytical curve, each having a preferred orientation in lattice plane (h 0 k 0 l 0 ) and having the same alloy composition as that of the hydrogen-absorbing alloy E to be evaluated, and a hydrogen-absorbing alloy S which is to be used as a standard and also has the same alloy composition, to X-ray diffractometry, to obtain integrated intensities of the diffraction peaks I M1 (h 1 k 1 l 1 ), I M2 (h 2 k 2 l 2 ), ···, I MX (h X k X l X ) and I S (h 1 k 1 l 1 ), I S (h 2 k 2 l 2 ), ···, I S (h X k X l X ) in optionally selected lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ), ··· , (h X k X l X ), respectively, obtaining the integrated intensity ratios I M1 (h 1 k 1 l 1 )/I S (h 1 k 1 l 1 ), I M2 (h 2 k 2 l 2 )/I S (h 2 k 2 l 2 ), ··· , I MX (h X k X l X )/I S (h X k X l X ) and the angles  1 ,  2 , ···,  X formed by the above lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ), ··· , (h X k X l X ) and the lattice plane (h 0 k 0 l 0 ), respectively, and substituting the obtained intensity ratios and angles for I(hkl)/I S (hkl) and  of the following formula (A), to obtain parameters P 1 , P 2 , ···, P X , each of which corresponds to a parameter P in a function F() satisfying the formula (A); (2) preparing an analytical curve showing the relationship between the P 1 , P 2 , ···, P X obtained above and observed values, T 1 , T 2 , ···, T X representing a property of the hydrogen-absorbing alloy for preparing analytical curve; (3) subjecting the hydrogen-absorbing alloy E to be evaluated to X-ray diffractometry, to obtain integrated intensities of the diffraction peaks I E1 (h E1 k E1 l E1 ), I E2 (h E2 k E2 l E2 ), ··· , I EY (h EY k EY l EY ) in optionally selected lattice planes (h E1 k E1 l E1 ), (h E2 k E2 l E2 ), ··· , (h EY k EY l EY ), respectively, obtaining the integrated intensity ratios I E1 (h E1 k E1 l E1 )/I S (h E1 k E1 l E1 ), I E2 (h E2 k E2 l E2 )/I S (h E2 k E2 l E2 ), ··· , I EY (h EY k EY l EY )/I S (h EY k EY l EY ) and the angles  E1 ,  E2 , ···,  EY formed by the above lattice planes (h E1 k E1 l E1 ), (h E2 k E2 l E2 ), ··· , (h EY k EY l EY ) and the lattice plane (h 0 k 0 l 0 ), respectively, and substituting the obtained intensity ratios and angles for I(hkl)/I S (hkl) and  of the following formula (A), to obtain a parameter P E for the hydrogen-absorbing alloy E to be evaluated; and (4) comparing the P E with the analytical curve to estimate the characteristics of the hydrogen-absorbing alloy E as an electrode material; F() = I(hkl)/I S (hkl) wherein I(hkl) is the integrated intensity of the X-ray diffraction peak in lattice plane (hkl) of the above hydrogen-absorbing alloys M 1 , M 2 , ···, M X for preparing analytical curve of the hydrogen-absorbing alloy E to be evaluated; I S (hkl) is the integrated intensity of the X-ray diffraction peak in lattice plane (hkl) of the standard hydrogen-absorbing alloy S; F() is a function of  and contains a parameter P which varies according to the structure of the hydrogen-absorbing alloys M 1 , M 2 , ···, M X for preparing analytical curve of the hydrogen-absorbing alloy E to be evaluated; and  is the angle (unit: radian) formed by the lattice plane (h 0 k 0 l 0 ) and the lattice plane (hkl). The method according to the present invention for evaluating hydrogen-absorbing alloys for electrode material is now explained in detail. Although the lattice planes (h E1 k E1 l E1 ), (h E2 k E2 l E2 ), ··· , (h EY k EY l EY ) may be different from those (h 1 k 1 l 1 ), (h 2 k 2 l 2 ), ···, (h X k X l X ), it is desirable that the two plane groups be wholly or partly the same. Then, with the same lattice planes, the integrated intensities of X-ray diffraction peaks of a standard hydrogen-absorbing alloy S obtained in step (1) can be used, as they are, as those that constitute the standard in step (3). The values of P 1 , P 2 , ···, P x in step (1) and the value P E in step (3) can be obtained for example as follows. The ratios of the integrated intensities of the X-ray diffraction peaks of hydrogen-absorbing alloys for preparing analytical curve of the hydrogen-absorbing alloy to be evaluated to those of a standard hydrogen-absorbing alloy are obtained for several 's, and putting the 's and the obtained integrated intensity ratios into the formula (A) [ F() = I(hkl)/I S (hkl)], to obtain simultaneous equations. The least square method is applied to each of the equations, to obtain most probable values, which give the P's. As described before, although there exists no distinct relationship between the composition or lattice constant of a hydrogen-absorbing alloy and the characteristics of the electrode obtained therefrom, there does exist a clear relationship between specific parameters obtained by analyzing data based on the results of X-ray diffractometry on the hydrogen-absorbing alloy to be evaluated and the characteristics of the electrode obtained therefrom. It becomes therefore possible to evaluate the characteristics of any hydrogen-absorbing alloy as follows. At first, X-ray diffractometry is carried out on a series of hydrogen-absorbing alloys and then the above parameters are obtained by mathematical calculation, such as by least square method, of the obtained data. An analytical curve showing the relationship between the above parameter and the battery characteristics is prepared. Then, simple comparison of the hydrogen-absorbing alloy to be evaluated with the analytical curve can rapidly evaluate the electrode characteristics, with no need of actually fabricating test batteries and conducting various tests thereon. In particular, where, as the function F() in the method of the present invention, the function with the parameter P being P A and P B as specified by the following formula (B) is used, it becomes possible to estimate the characteristics of electrodes, such as the degree of activation, capacity retention ratio after charge-discharge cycles, corrosive resistance and capacity, more precisely and in the same degrees as those obtainable in the actual running test of batteries fabricated with the electrodes. F() = P A + (1 - P A )exp(-P B ·  2 ) wherein P A and P B are parameters in the present invention, which vary corresponding to the alloy compositions of the hydrogen-absorbing alloys for preparing analytical curve, M 1 , M 2 , ···, M X and the hydrogen-absorbing alloy E to be evaluated and determine their characteristics as electrode materials, thus corresponding to the parameter P in the present invention; and  is the angle (unit: radian) formed by the lattice plane (h 0 k 0 l 0 ) and the lattice plane (hkl). Examples of hydrogen-absorbing alloys which can suitably evaluated by the method of the present invention are the same as already mentioned as usable for the hydrogen-absorbing alloy electrodes of the present invention. Other features of the invention will become more apparent in the course of the following detailed descriptions of exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof. EXAMPLES Example 1 [Preparation of hydrogen-absorbing alloy] There were mixed a commercially available Mm (Misch metal: mixture of rare earth elements), Ni, Co, Mn and Al in an elemental ratio of 1.0:3.1:0.9:0.6:0.4 and the mixture was melted in an arc melting furnace under an argon atmosphere. The alloy melt thus obtained by arc melting was solidified by dropping onto a roll rotating at a high roll surface speed (liquid quenching method) of 1 x 10 3 cm/sec, 2 x 10 3 cm/sec, 3 x 10 3 cm/sec, 4 x 10 3 cm/sec, 5 x 10 3 cm/sec or 6 x 10 3 cm/sec, to give hydrogen-absorbing alloys AL1 through AL6, in this order, having a composition of MmNi 3.1 Co 0.9 Mn 0.6 Al 0.4 . Separately, a standard alloy having the same compsition and having no preferred orientation was prepared by allowing part of the above alloy melt to cool into an alloy block, pulverizing the alloy block into particles having an average diameter of 10 to 30µm, then heat treating the particles at 800°C under vacuum for 24 hours and allowing the treated particles to cool to room temperature. [Calculation of parameters P A and P B ] The hydrogen-absorbing alloys AL1 through AL6 and the standard hydrogen-absorbing alloy having no preferred orientation were analyzed by X-ray diffractometry. From the obtained patterns, integrated intensities in various lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ), ···, (h X K X l X ) were obtained and their ratios to that of the standard were calculated. These ratios were substituted for I(hkl)/I S (hkl) and the angles  1 ,  2 , ···,  X formed by the preferred orientation plane (110) and the lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ), ···, (h X K X l X ) for  in the above formula (B). From the thus obtained simultaneous equations, parameters P A 's and P B 's which relate to the preferred orientation (alloy structure) of the hydrogen-absorbing alloys (see H. Toraya and F. Maruo, Mineralogical Journal, Vol. 10 (1981) 211) were obtained by the non-linear least square method. Although this Example used, as a standard hydrogen-absorbing alloy, one having no preferred orientation, which is not a must, those having a preferred orientation may also be used. The results are shown in Table 1. Alloy Roll surface speed (cm/sec) P A P B AL1 1 x 10 3 0.75 12.5 AL2 2 x 10 3 0.73 12.8 AL3 3 x 10 3 0.70 13.2 AL4 4 x 10 3 0.67 13.6 AL5 5 x 10 3 0.63 14.1 AL6 6 x 10 3 0.58 14.6 [Preparation of test cells] The hydrogen-absorbing alloys AL1 through AL6 were mechanically pulverized into powders each having an average particle diameter of about 150µm. Six alloy pastes were then prepared by mixing 1 g of each of the alloy powders, 1.2 g of nickel powder as a conductive agent and 0.2 g of polytetrafluoroethylene (PTFE) as a binder and rolling the mixtures. A prescribed amount of each of the alloy pastes was wrapped with a nickel mesh and pressed, to give disc-shaped hydrogen-absorbing alloy electrodes A1 through A6 having a diameter of 20 mm. Test cells similar to those shown in FIGURE 1 were fabricated with each of the above hydrogen-absorbing alloy electrodes as a test electrode (action electrode), a counter electrode of a cylindrical sintered nickel electrode having a sufficiently large electrochemical capacity compared to the test electrodes, and a reference electrode of a plate-shaped sintered nickel electrode, and an electrolyte of 30% by weight aqueous potassium hydroxide solution. [Evaluation of capacity retention ratio] The test cells were subjected to repeated cycles of charging at a current of 20 mA/g for 15 hours, resting for 1 hour, then discharging to a discharge termination voltage of 1.0 V and then resting for 1 hour, at room temperature (25°C), to obtain capacity retention ratios (%) at the 100-th cycle. The capacity retention ratio herein means the ratio of the capacity obtained above to the maximum capacity (100%). FIGURES 2 and 3 show the relationship between the capacity retention ratio of each the test electrodes thus obtained by actual measurement and the parameter P A and P B , respectively, obtained on the hydrogen-absorbing alloys AL1 through AL6. FIGURE 2 is a graph with the ordinate representing the capacity retention ratio and abscissa the parameter P A , while FIGURE 3 is a graph with the same ordinate and with the abscissa representing the parameter P B . FIGURES 2 and 3 clearly show that there exists a nearly primary functional (linear) relationship between the capacity retention ratio obtained by actual observation and the parameter P A or P B on each of the hydrogen-absorbing alloys. The following method was used in order to estimate the capacity retention ratio of the test electrodes from the parameter P A or P B . Analytical curves (linear lines) showing the relationship between the capacity retention ratios obtained by actual observation on the test electrodes A1, A3 and A6, and the parameter P A or P B were obtained by the non-linear least square method. These analytical lines were drawn in solid lines in FIGURES 2 and 3. Then, the capacity retention ratios of the test electrodes A2, A4 and A5 were estimated from the analytical lines thus drawn and compared with those obtained by actual observation. The estimation was conducted by locating, on the analytical lines, the points corresponding to the abscissa values of P A 's or P B 's of the hydrogen-absorbing alloys AL2, AL4 and AL5 and reading the ordinate values of the points. The results are shown in Table 2. Test electrode Capacity retention ratio (%) Observed Estimated from P A Estimated from P B A1 81.5 - - A2 82.5 82.2 82.2 A3 83.1 - - A4 83.4 83.5 83.4 A5 84.5 84.4 84.2 A6 85.2 - - Table 2 shows that the capacity retention ratios of each of the test electrodes A2, A4 and A5 estimated from the analytical lines are very close to that obtained by actual observation. It is understood from this test that the use of parameter P A or P B realizes a very precise estimation of capacity retention ratio. [Evaluation of degree of activation] The test cells were charged at 20 mA/g for 15 hours, rested for 1 hour and then discharged at 100 mA/g to a discharge termination voltage of 1.0 V, to give a discharge capacity of C 1 . The cells were then discharged at 20 mA/g to a discharge termination voltage of 1.0 V, to give a discharge capacity C 2 . The degree of activation (%) of each cell was obtained from the discharge capacities C 1 and C 2 by the following formula. Degree of activation = C 1 /(C 1 + C 2 ) x 100 FIGURES 4 and 5 show the relationship between the degree of activation of each of the test electrodes thus obtained and the parameter P A and P B , respectively, previously obtained on the hydrogen-absorbing alloys AL1 through AL6. FIGURE 4 is a graph with the ordinate representing the degree of activation and abscissa the parameter P A , while FIGURE 5 is a graph with the same ordinate and with the abscissa representing the parameter P B . FIGURES 4 and 5 clearly show that there exists a nearly primary functional (linear) relationship between the degree of activation obtained by actual observation and the parameter P A or P B on each of the hydrogen-absorbing alloys. The following method was used in order to estimate the degree of activation of the test electrodes from the parameter P A or P B . Analytical curves (linear lines) showing the relationship between the degrees of activation obtained by actual observation on the test electrodes A1, A3 and A6 and the parameter P A or P B were obtained by the non-linear least square method. These analytical lines were drawn in solid lines in FIGURES 4 and 5. Then, the degree of activation of the test electrodes A2, A4 and A5 were estimated from the analytical lines thus drawn and compared with those obtained by actual observation. The estimation was conducted by locating, on the analytical lines, the points corresponding to the P A 's or P B 's of the hydrogen-absorbing alloys AL2, AL4 and AL5 and reading the ordinate values of the points. The results are shown in Table 3. Test electrode Degree of activation (%) Observed Estimated from P A Estimated from P B A1 75.8 - - A2 75.1 75.0 75.0 A3 73.9 - - A4 72.5 72.7 72.5 A5 70.7 71.2 70.9 A6 69.3 - - Table 3 shows that the degree of activation of each of the test electrodes A2, A4 and A5 estimated from the analytical lines are very close to that obtained by actual observation. It is understood from this test that the use of parameter P A or P B realizes a very precise estimation of degree of activation. Example 2 [Preparation of hydrogen-absorbing alloy] There were mixed Ti, Zr, Ni, Co, V and Mn in an elemental ratio of 0.5:0.5:1.0:0.2:0.5:0.3 and the mixture was melted in an arc melting furnace under an argon atmosphere. The alloy melt thus obtained by arc melting was solidified by dropping onto a roll rotating at a high roll surface speed (liquid quenching method) of 1 x 10 3 cm/sec, 2 x 10 3 cm/sec, 3 x 10 3 cm/sec, 4 x 10 3 cm/sec, 5 x 10 3 cm/sec or 6 x 10 3 cm/sec, to give hydrogen-absorbing alloys AL7 through AL12, in this order, having a composition of Ti 0.5 Zr 0.5 NiCo 0.2 V 0.5 Mn 0.3 . Separately, a standard alloy having the same composition and having no preferred orientation was prepared by allowing part of the above alloy melt to cool into an alloy block, pulverizing the alloy block into particles having an average diameter of 10 to 30µm, then heat treating the particles at 800°C under vacuum for 24 hours and allowing the treated particles to cool to room temperature. [Calculation of parameters P A and P B ] The hydrogen-absorbing alloys AL7 through AL12 and the standard hydrogen-absorbing alloy having no preferred orientation were analyzed by X-ray diffractometry. From the obtained patterns, integrated intensities in various lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ), ···, (h X K X l X ) were obtained and their ratios to that of the standard were calculated. These ratios were substituted for I(hkl)/I S (hkl) and the angles  1 ,  2 , ···,  X formed by the preferred orientation planeplane (002) and the lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ), ···, (h X K X l X ) for  in the above formula (B). From the thus obtained simultaneous equations, parameters P A 's and P B 's which relate to the preferred orientation (alloy structure) of the hydrogen-absorbing alloys were obtained by the non-linear least square method. The results are shown in Table 4. Alloy Roll surface speed (cm/sec) P A P B AL7 1 x 10 3 0.88 9.7 AL8 2 x 10 3 0.85 9.9 AL9 3 x 10 3 0.83 10.4 AL10 4 x 10 3 0.77 11.2 AL11 5 x 10 3 0.74 11.7 AL12 6 x 10 3 0.69 12.5 [Evaluation of capacity retention ratio] Example 1 was repeated except that the above hydrogen-absorbing alloy electrodes AL7 through AL12 were used as test electrodes, to fabricate test cells. The test cells were subjected to repeated cycles of charging at a current of 30 mA/g for 8 hours, resting for 1 hour, then discharging to a discharge termination voltage of 1.0 V and then resting for 1 hour, at room temperature (25°C). After 100 cycles, the cells were checked for the capacity retention ratio (%). FIGURES 6 and 7 show the relationship between the capacity retention ratio of each the test electrodes thus obtained and the parameter P A and P B , respectively, obtained on the hydrogen-absorbing alloys AL7 through AL12. FIGURE 6 is a graph with the ordinate representing the capacity retention ratio and abscissa the parameter P A , while FIGURE 7 is a graph with the same ordinate and with the abscissa representing the parameter P B . FIGURES 6 and 7 clearly show that there exists a nearly primary functional (linear) relationship between the capacity retention ratio obtained by actual observation and the parameter P A or P B on each of the hydrogen-absorbing alloys. The following method was used in order to estimate the capacity retention ratio of the test electrodes from the parameter P A or P B . Analytical curves (linear lines) showing the relationship between the capacity retention ratios obtained by actual observation on the test electrodes A7, A9 and A12 and the parameter P A or P B were obtained by the non-linear least square method. These analytical lines were drawn in solid lines in FIGURES 6 and 7. Then, the capacity retention ratios of the test electrodes A8, A10 and A11 were estimated from the analytical lines thus drawn and compared with those obtained by actual observation. The estimation was conducted by locating, on the analytical lines, the points corresponding to the abscissa values of P A 's or P B 's of the hydrogen-absorbing alloys AL8, AL10 and AL11 and reading the ordinate values of the points. The results are shown in Table 5. Test electrode Capacity retention ratio (%) Observed Estimated from P A Estimated from P B A7 55.4 - - A8 56.1 56.5 56.1 A9 57.5 - - A10 58.5 58.9 58.7 A11 60.3 59.7 59.6 A12 61.1 - - Table 5 shows that the capacity retention ratios of each of the test electrodes A8, A10 and A11 estimated from the analytical lines are very close to that obtained by actual observation. It is understood from this test that the use of parameter P A or P B realizes a very precise estimation of capacity retention ratio. [Evaluation of degree of activation] The degree of activation (%) of each of the test cells was obtained in the same manner as in Example 5, i.e. under the same charge-discharge conditions. FIGURES 8 and 9 show the relationship between the degree of activation of each the test electrodes thus obtained and the parameter P A and P B , respectively, obtained on the hydrogen-absorbing alloys AL7 through AL12. FIGURE 8 is a graph with the ordinate representing the degree of activation and abscissa the parameter P A , while FIGURE 9 is a graph with the same ordinate and with the abscissa representing the parameter P B . FIGURES 8 and 9 clearly show that there exists a nearly primary functional (linear) relationship between the degree of activation obtained by actual observation and the parameter P A or P B on each of the hydrogen-absorbing alloys. The following method was used in order to estimate the degree of activation of the test electrodes from the parameter P A or P B . Analytical curves (linear lines) showing the relationship between the degrees of activation obtained by actual observation on the test electrodes A7, A9 and A12 and the parameter P A or P B were obtained by the non-linear least square method. These analytical lines were drawn in solid lines in FIGURES 8 and 9. Then, the degree of activation of the test electrodes A8, A10 and A11 were estimated from the analytical lines thus drawn and compared with those obtained by actual observation. The estimation was conducted by locating, on the analytical lines, the points corresponding to the abscissa values of P A 's or P B 's of the hydrogen-absorbing alloys AL8, AL10 and AL11 and reading the ordinate values of the points. The results are shown in Table 6. Test electrode Degree of activation (%) Observed Estimated from P A Estimated from P B A7 63.5 - - A8 61.5 60.6 61.3 A9 57.6 - - A10 56.1 56.7 57.0 A11 53.9 55.2 55.4 A12 53.3 - - Table 6 shows that the degree of activation of each of the test electrodes A8, A10 and A11 estimated from the analytical lines are very close to that obtained by actual observation. It is understood from this test that the use of parameter P A or P B realizes a very precise estimation of degree of activation. As shown in Examples 1 and 2, it is possible to estimate the electrode characteristics of a hydrogen-absorbing alloy by using a common analytical curve, as long as the hydrogen-absorbing alloy has the same composition as those used for preparing the analytical curve. However, to evaluate a hydrogen-absorbing alloy having a different composition, it becomes necessary to prepare a new analytical curve with those having the same composition. Although Examples 1 and 2 gave explanations while mentioning, as hydrogen-absorbing alloy to be evaluated, MmNi 3.1 Co 0.9 Mn 0.6 Al 0.4 and Ti 0.5 Zr 0.5 NiCo 0.2 V 0.5 Mn 0.3 , any type of hydrogen-absorbing alloy can be evaluated by the method of the present invention. Although Examples 1 and 2 dealt with application of the method of the invention to the evaluation of capacity retention ratio and degree of activation, the method of the present invention can also be applied suitably to other electrode characteristics, such as corrosive resistance and initial capacity. Although Examples 1 and 2 used as a function F() satisfying the function F() = I(hkl)/I S (hkl), F() = P A + (1 - P A )exp(-P B · 2 ), any function that determines the electrode characteristics via specific parameters can be used in the method of the invention, with no particular limitation.

Claims: A method for evaluating a hydrogen-absorbing alloy E as an electrode material, comprising the steps of: (1) measuring integrated intensities of X-ray diffraction peaks I M1 , I M2 , ..., I MX in various lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ),..., (h x k x l x ) for a plurality of hydrogen-absorbing alloys M 1 , M 2 ,..., M X each having a preferred orientation in lattice plane (h 0 k 0 l 0 ) and having the same alloy composition as the hydrogen-absorbing alloy E, and measuring integrated intensities of X-ray diffraction peaks I S (h 1 k 1 l 1 ), I S (h 2 k 2 l 2 ),..., I S (h x k x l x ) in lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ),..., (h x k x l x ), respectively, for a hydrogen-absorbing alloy S having the same alloy composition as the hydrogen-absorbing alloy E, (1.1) determining integrated intensity ratios I M1 /I S , I M2 /I S ,..., I MX /I S for the various lattice planes and angles  1 ,  2 ,...,  X formed by these lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ),..., (h x k x l x ) and the lattice plane (h 0 k 0 l 0 ), respectively, and (1.2) determining a parameter P, which varies according to a structure of the plurality of hydrogen absorbing alloys M 1 , M 2 ,..., M X , and is a parameter of said function F(), where: F() = I(hkl)/I S (hkl) wherein I(hkl) is an integrated intensity of the X-ray diffraction peak in lattice plane (hkl) of the plurality of hydrogen-absorbing alloys M 1 , M 2 ,..., M X ; I S (hkl) is an integrated intensity of the X-ray diffraction peak in lattice plane (hkl) of the hydrogen-absorbing alloy S; and  is an angle formed by the lattice plane (h 0 k 0 l 0 ) and the lattice plane (hkl); (2) determining an analytical curve as a relationship between the parameter P and observed values, T 1 , T 2 ..., T X representing at least one property of the plurality of hydrogen-absorbing alloys M 1 , M 2 ,..., M X as an electrode material; (3) measuring integrated intensities of X-ray diffraction peaks I E1 (h E1 k E1 l E1 ), I E2 (h E2 k E2 l E2 ),..., I EY (h EY k EY l EY ) in lattice planes (h E1 k E1 l E1 ), (h E2 k E2 l E2 ),..., (h EY k EY l EY ), respectively, for the hydrogen-absorbing alloy E, (3.1) determining integrated intensity ratios I E1 (h E1 k E1 l E1 )/ I S (h E1 k E1 l E1 ), I E2 (h E2 k E2 l E2 )/I S h E2 k E2 l E2 ),..., I EY (h EY k EY I EY )/ I S (h EY k EY l EY ) and angles  E1 ,  E2 ,...,  EY formed by the lattice planes (h E1 k E1 l E1 ), (h E2 k E2 l E2 ),..., (h EY k EY l EY ) and the lattice plane (h 0 k 0 l 0 ) respectively, and (3.2) determining a parameter P E for the hydrogen-absorbing alloy E by substituting the determined integrated intensity ratios and angles for I(hkl)/I S (hkl) and  in formula (A); and (4) determining the value of said at least one property of the hydrogen-absorbing alloy E with the parameter P E from said analytical curve obtained in step (2). A method for evaluating a hydrogen-absorbing alloy E as an electrode material, comprising the steps of: (1) measuring integrated intensities of X-ray diffraction peaks I M1 , I M2 ,..., I MX in various lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ),..., (h x k x l x ) for a plurality of hydrogen-absorbing alloys M 1 , M 2 ,..., M X each having a preferred orientation in lattice plane (h 0 k 0 l 0 ) and having the same alloy composition as the hydrogen-absorbing alloy E, and measuring integrated intensities of X-ray diffraction peaks I S (h 1 k 1 l 1 ), I S (h 2 k 2 l 2 ),..., I S (h x k x l x ) in lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ),...,(h x k x l x ), respectively, for a hydrogen-absorbing alloy S having the same alloy as the hydrogen-absorbing alloy E, (1.1) determining integrated intensity ratios I M1 /I S , I M2 /I S ,..., I MX /I S for the various lattice planes and angles  1 ,  2 ,...,  X formed by these lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ),..., (h x k x l x ) and the lattice plane (h 0 k 0 l 0 ), respectively, and (1.2) determining the parameters P A and P B which varies according to a structure of the plurality of hydrogen absorbing alloys M 1 , M 2 ,..., M X , and are parameters of said function F(), where: F() = P A + (1-P A )exp(-P B  2 ) = I(hkl)/I S (hkl) wherein I(hkl) is an integrated intensity of the X-ray diffraction peak in lattice plane (hkl) of the plurality of hydrogen-absorbing alloys M 1 , M 2 ,..., M X ; I S (hkl) is an integrated intensity of the X-ray diffraction peak in lattice plane (hkl) of the hydrogen-absorbing alloy S; and  is an angle formed by the lattice plane (h 0 k 0 l 0 ) and the lattice plane (hkl); (2) determining an analytical curve as a relationship between the parameters P A and/or P B and observed values, T 1 , T 2 ..., T X representing at least one property of the plurality of hydrogen-absorbing alloys M 1 , M 2 ,..., M X as an electrode material; (3) measuring integrated intensities of X-ray diffraction peaks I E1 (h E1 k E1 l E1 ), I E2 (h E2 k E2 l E2 ),..., I EY (h EY k EY l EY ) in lattice planes (h E1 k E1 l E1 ), (h E2 k E2 l E2 ),..., (h EY k EY l EY ), respectively, for the hydrogen-absorbing alloy E, (3.1) determining integrated intensity ratios I E1 (h E1 k E1 l E1 )/ I S (h E1 k E1 l E1 ), I E2 (h E2 k E2 l E2 )/I S (h E2 k E2 l E2 ),..., I EY (h EY k EY l EY )/ I S (h EY k EY l EY ) and angles  E1 ,  E2 ,...,  EY formed by the lattice planes (h E1 k E1 l E1 ), (h E2 k E2 l E2 ),..., (h EY k EY l EY ) and the lattice plane (h 0 k 0 l 0 ), respectively, and (3.2) determining parameters P EA and/or P EB for the hydrogen-absorbing alloy E, by substituting the determined integrated intensity ratios and angles for I(hkl)/I S (hkl) and  in formula (B); and (4) determining the value of said at least one property of the hydrogen-absorbing alloy E with the parameters P EA and/or P EB from said analytical curve obtained in step (2). The method of Claim 1 or 2, wherein the lattice planes (h E1 k E1 l E1 ), (h E2 k E2 l E2 ), ..., (h EY k EY l EY ) are equal to the lattice planes (h 1 k 1 l 1 ), (h 2 k 2 l 2 ),..., (h x k x l x ), respectively.

Inventors: FUJITANI SHIN, ISONO TAKAHIRO, NAKAMURA HIROSHI, NAKAMURA YUMIKO, WATANABE HIROSHI, YONEZU IKUO, FUJITANI, SHIN, ISONO, TAKAHIRO, NAKAMURA, HIROSHI, NAKAMURA, YUMIKO, WATANABE, HIROSHI, YONEZU, IKUO
Applicants: SANYO ELECTRIC CO, SANYO ELECTRIC CO. LTD
Application year: 1994
Main classification: H01M4
IPC codes: H01M4, C01B3